Bucket Teeth for Backhoe PC220-6LR For PC220 4HOLES Replacement Parts

Rock Hardness Classification Standards and Their Impact on Loosening Tooth Selection

Rock hardness is a critical factor in determining loosening tooth selection. The engineering field commonly adopts the Rockwell hardness coefficient (f value) as the classification standard. This coefficient is calculated based on the uniaxial ultimate compressive strength of rock (f = R/100, where R is in kg/cm²), dividing rock hardness into 10 grades:

Rock Grade    Hardness Level    Representative Rocks    Hardness Coefficient (f)

Ⅰ    Most Solid    Quartzite, Basalt    f=20

Ⅱ    Very Solid    Granite, Most Solid Sandstone and Limestone    f=15

Ⅲ    Solid    Dense Granite, Very Solid Sandstone    f=10

Ⅳa    Fairly Solid Sandstone Shale, Shale-like Sandstone    f=5

Ⅴa    Moderately Firm    Various Soft Shales    f=3

In mining operations, granite falls under the Very Firm category (f=15), while shale ranges from Fairly Firm (f=5) to Moderately Firm (f=3) depending on specific types. These hardness variations directly influence the material selection and quantity configuration of ripper teeth.